A little while ago I wrote a post about climate change targets in which I suggested that the internationally agreed temperature limit of 2°C was a somewhat arbitrary figure to choose as a target for the maximum temperature we are prepared to tolerate. Hansen’s latest paper makes the case for a temperature limit of just 1°C because he says 2°C would activate slow feedbacks in the climate system and result in dangerous warming of 3-4°C.

So what are the dangerous impacts he’s talking about? Some of these are food shortages, extreme weather events, an increase in extreme summer heat, world sea level rise, ocean acidification and scarcity of water supplies. Hansen describes the climate impacts of a 2°C warmer world as “disastrous”.

I know that for many people 2°C doesn’t sound like very much. After all, our local temperatures vary by much more than 2°C on a day-to-day basis. But a 5°C change in the other direction was enough to “bury a large part of North America” under a thick blanket of ice some 20,000 years ago. During the Eemian period, the interglacial which began 130,000 years ago, the Earth was ~2°C warmer than today and with a sea level peak of 9m above present. That’s a death sentence for many of today’s cities.

Once the temperature has increased we’re stuck with it for a long time – centuries – because the oceans suck up so much heat and transfer it to their depths. The Antarctic and Greenland ice sheets took thousands of years to grow and once they melt, cannot be refrozen so easily. The loss of these ice sheets would raise the sea level by many metres wiping out coastal cities around the world. Paleoclimate data tells us that sea level has risen as fast as one metre per century in the past and we are currently increasing greenhouse gas emissions at a rate not seen before.

But it doesn’t have to be all doom and gloom. If we stopped emissions in 2015, CO2 would decline to 350ppm (we are currently at 395ppm) by the end of the century due to natural sinks – ocean, land and biosphere – that suck it up. If we wait 20 years, then we won’t see a return to 350ppm until 2300. If we wait 40 years, it will take until after 3000 before we see a return to 350ppm. The longer we delay action, the harder the problem is to solve.

Had we started tackling this problem in 2005, an emissions reduction of just 3.5% per year would have led us to 350ppm by 2100. But we didn’t. Now we would need to reduce emissions by 6% per year. If we wait until 2020, we will need to reduce emissions by 15% per year.

By studying how Earth’s climate has changed in the past, Hansen gives his best estimate for climate sensitivity – the amount of warming we can expect per doubling of CO2 – which is close to 3°C. We are expected to reach this point of doubling by mid-century. This doesn’t mean the temperature will have increased 3°C by mid-century because there’s an inertia in the climate system and it will take a little while for it to catch up. But this is the pathway we will have carved for ourselves and our children. It’s worth mentioning that this calculation for climate sensitivity is made with paleoclimate data and is independent of climate models.

He discusses aspects of policy and supports a carbon tax, improvements in energy efficiency and expansion of renewable energies and nuclear power. He also expects reforestation and improved agricultural and forestry practices to absorb some CO2. If the two biggest emitters – China, USA – implement a carbon tax, others will follow suit because those two could impose a border duty on products from countries without a carbon tax.

He also discusses removing CO2 from the atmosphere with geoengineering to highlight the cost and difficulty of doing this. If we could turn 1 GtC (gigatonne) of CO2 into a brick (and note that we have emitted 531 GtC so far and counting) it would produce the volume equivalent of about 3000 Empire State buildings. It is possible, according to Hansen, that with a carbon tax, or some other financial incentive, we may develop the technology to do this efficiently and cost-effectively but the technology is not available today.

Hansen pitches the problem as a moral one of intergenerational ethics and I agree with him on this. The idea here is that future generations will inherit a climate situation that is spiralling out of control but for which they are not to blame. Yet they have a fundamental right to inhabit a liveable planet.

Although the paper is about impending disaster, it is only a disaster if we do nothing. Hansen ends with the conviction that this is not an insurmountable problem. It can be solved if we take appropriate steps today and he makes clear in the paper what these steps are: a rising fee on fossil fuel emissions, reforestation and improvements in agricultural and forestry practices and widespread adoption of renewable and carbon-free energy.

And while they are the big two, I would hope some other countries, with a better record for strong action to this point, like Japan and the EU, might be persuaded to act as well. That would make the pressure even stronger.

Which is why the World Trade Organisation forbids taking the environment into account. That would be an illegal trade barrier, as far as I understand. Thus first we need to get rid of the WTO, if they keep behaving like this.

Victor, I didn’t realise this was the case so I’ve just gone and had a little search and there do appear to be some world trade rules standing in the way. I’ve found this paper from 2009 which may be a little dated now, but towards the end they say:

As discussed in this article, carbon taxes and related national GHG-emission control schemes applying to imported products will be subject to GATT and WTO Agreement rules and disciplines, including national treatment requirements and the rules against import restrictions. Notwithstanding international treaties such as the UNFCCC and the Kyoto Protocol, WTO Member States still have to justify carbon-reduction measures applied at the border under the applicable provisions of the GATT, including the non-discrimination and other provisions set out in the agreement.

There are significant areas of uncertainty in terms of how these GATT-based rules will operate, however, notably in cases where GHG-reduction measures and regulations apply to the production processes and methods used to make imported goods. While the GATT contains important exceptions that permit departures from national treatment and other obligations, it is not clear how far these exceptions apply. While GATT and WTO case law has assisted in clarifying some of these points, considerable uncertainty remains.

“Had we started tackling this problem in 2005, an emissions reduction of just 3.5% per year would have led us to 350ppm by 2100. But we didn’t. Now we would need to reduce emissions by 6% per year. If we wait until 2020, we will need to reduce emissions by 15% per year.”

In this way the climate ostriches by delaying action are provoking the more drastic measures they fear so much.

I think the two most poignant parts of this post are your reference to the exponentially escalating costs of “business as usual” and the fact that the changes we are making to the planet will be with us for a long, long time.

I think that many people feel that we can just fix this problem with some as-yet-developed technology. But there is no superman or super-tech that will come and just save us. The best way to save ourselves is an aggressive policy of prevention 🙂

Also, to put your temperature change into perspective, there is some evidence now that the rise of our global civilization may have been predicated on an almost unheard of period of temperature stability that has lasted the last 12 thousand years or so:

That’s a good article in the Guardian, thanks. It’s true that we have prospered in a relatively stable climate. Our society is now so advanced but we still rely on growing crops for food. As you’ve written yourself, changing weather patterns lead to crop failures which leads to famine which leads to conflict which is disastrous.

I thought Hansen’s calculations for a return to 350ppm under different scenarios was very useful i.e. if we stop emissions in 2015 we’re back to 350ppm by the end of the century. Yet a delay of 40 years will take us 3000 years to return to 350ppm. Business as usual looks like the craziest option when you view it that way.

I’m glad you’re writing on this RachelWe . I didn’t know the term paleoclimate data so I looked it up. Seems it means pretty much what it sounds like it means.

Hansen’s point (and yours) that this problem is a moral one of intergenerational ethics is a point that needs to be emphasized whenever we get a chance. Maybe people will begin to relate to that — that future generations have a right to a liveable, but if we continue, “this is the pathway we will have carved for ourselves and our children.”

As you know, I am a firm believer that if we stop eating meat — and hence stop clearing forests for grazing land and for monoculture to feed animals — we could solve this problem. But too many people either don’t see the connection, or don’t care enough to make the change. We must teach (and learn) that we are in fact a part of the web of all life.

[…] greenhouse gases continue to accumulate in the atmosphere. Last month I wrote about a new paper, Dangerous Climate Change, which said that if we stopped emissions in 2015, CO2 would return to the safer level of 350ppm by […]